Wireless communications systems are used in a variety of telecommunications systems, television, radio and other media systems, data communication networks, and other systems to convey information between remote points using wireless transmitters and wireless receivers. A transmitter is an electronic device which, usually with the aid of an antenna, propagates an electromagnetic signal such as radio, television, or other telecommunications. Transmitters often include signal amplifiers which receive a radio-frequency or other signal, amplify the signal by a predetermined gain, and communicate the amplified signal. On the other hand, a receiver is an electronic device which, also usually with the aid of an antenna, receives and processes a wireless electromagnetic signal. In certain instances, a transmitter and receiver may be combined into a single device called a transceiver.
Receivers include a number of components that are arranged to convert a received wireless signal, usually in the radio-frequency spectrum, to a digital signal capable of being processed by digital circuitry (e.g., microprocessors, digital signal processors, etc.). Selected components of a traditional receiver are shown in FIG. 6. As shown in FIG. 6, a traditional receiver 600 may include a bandpass filter 605 and a low-noise amplifier (LNA) 610 to amplify a received radio-frequency (RF) signal. The amplified RF signal may then be frequency downconverted by a downconverter 620 based on a local-oscillator signal produced by oscillator 630. The downconverted signal may then be filtered by low-pass filter 640, providing a low-pass filtered analog signal at its output. This analog signal may be converted to a digital signal by analog-to-digital converter (ADC) 650. Such digital signal may then be communicated to digital circuitry for further processing.
In such traditional receiver designs, the downconverter 620 may be implemented by a mixer having a metal-oxide semiconductor field-effect transistor (MOSFET), wherein the RF signal passes through the conducting terminals of the MOSFET while the gate of the MOSFET is driven with the local-oscillator signal. During the phase of the local-oscillator signal that turns the MOSFET on, the RF signal will pass through the MOSFET. During the on phase of the oscillation signal, the voltage at the gate of the MOSFET is traditionally held steady by the local-oscillator signal, and the voltage at the conducting terminals of the MOSFET will vary with the RF signal. Therefore, during the on phase of the local-oscillator signal, the gate-to-source voltage of the MOSFET will vary as the voltage potential of RF signal varies. Accordingly, during the on phase of the local-oscillator signal, the resistance (Ron) of the MOSFET will vary with the RF signal as the RF signal passes through the MOSFET. The varying Ron will add a nonlinear component to the signal being passed through the MOSFET during the downconversion.
Transmitters include a number of components that are arranged to convert a digital signal to a wireless signal in the radio frequency spectrum. A traditional transmitter may include a digital-to-analog converter (DAC) to convert the digital signal into an analog signal, and an upconverter to frequency upconvert the analog signal into a frequency spectrum that can be wirelessly transmitted. Similar to the downconverter discussed above, the upconverter may be implemented with a MOSFET, wherein the analog signal passes through the conducting terminals of the MOSFET while the gate of the MOSFET is driven with the oscillation signal. Accordingly, a traditional transmitter may experience the similar nonlinear effects due to a varying Ron as a signal is passed through the conducting terminals of a MOSFET during upconversion.